"Entanglement consists of quantum correlations between distinct subsystems (or modes). This physical property may lead to the superiority of quantum information processors over their classical counterparts to perform certain tasks, like performing physical simulations and prime number factoring. Therefore, the production of large entangled states is a relevant challenge for possible implementations of the ideas issued by the quantum information theory.

Looking for the matter of size, we have shown that a simple laser source, known as the optical parametric oscillator, can generate a set of six entangled modes. Even in its most basic configuration, consisting of a single crystal placed between two mirrors, it presents a rich dynamics of photon pair generation and photon exchange between modes associated to different frequencies of the electromagnetic field. Although previous works have shown entanglement between two or three modes on these oscillators, the structure we have demonstrated doubles the available space for information processing. The new tools we present can be further applied in more elaborated systems, extending their computational power, and on the development of new entangled sources in the optical domain."